This invention relates to construction of friction piles or friction pile-like structures for supporting and under-pinning structures on stable and unstable base soils, and for construction of shoring system(s) in stable and unstable base soils as for example:
(A) preparation of foundation support systems for buildings, walks, bridge abutments, concrete roads, and other structures requiring a base support system;
(B) construction of an in-situ barrier to prevent collapse or sloughing of native soils within a delineated perimeter foot print or face where excavation is to be undertaken;
(C) construction of vertical support members in perma-frost or ice-lensed soils which bear the loading of residential, commercial, industrial buildings, pipelines, or any other structures requiring the utilization of this type of foundation support system;
(D) construction of an anchoring or pinning system to which road beds, walks, and other such structures can be anchored to prevent horizontal movement of base soils beneath these structures.
In typical construction of foundation support systems where piles are needed or where piles are needed to construct a structural floor or structural concrete slab, friction piles are employed. Friction piles are typically either of the driven or drilled type. The latter system employs the drilling of a pre-determined size of hole which is filled with concrete and left to cure and thereby forming a friction pile. This pile may or may not be re-enforced with steel re-enforcing-bar. Alternatively, steel members, wooden timbers or poles, or synthetic members are manually driven into base soils to pre-determined depths with a resultant friction pile being formed. A system or array of such piles are put in place to support and eliminate or minimize future settlement of whatever structure is to be constructed on the system of piles.
In certain construction situations barriers are required to be driven into the base soils to prevent sloughing of base soils as the soils on one side of the barrier are excavated for a foundation, installation of a pipeline, etc. Typically, these barriers are sheets of steel that are mechanically driven into the base soils and which can be joined to each other through a tongue and groove like linkage at the ends of the steel sheets. Typically this is referred to as placement of sheet piling. The sheet piling can also be constructed of sheets of synthetic materials. Alternatively, steel, wooden or synthetic members or poles may be driven into base soils adjacent to each other to prevent sloughing.
Typically in base soils where perma frost or ice lensing is a condition, vertical support members are driven or drilled into the base soils to support a building, pipeline or other structure. Typically, wooded members are driven into the base soils to provide a friction pile. Wood members are used as the thermal conductivity of wood is low. Steel members can also be used but steel has a high thermal conductivity and more susceptible to result in settlement as heat is transferred through the steel member and the perma frost degrades. Vertical support members can also be installed by firstly drilling a hole, inserting a wooden or metal member and back filling around the member with a slurry which either freezes in place or sets up and cures in the case of certain cementitious slurries.
Under certain construction circumstances, friction piles can be used to tie-in adjacent horizontal structures such as gravel, asphalt concrete or concrete roads to prevent them from moving. Movement of such structures is typically as a result of a slip face in the base soils that may be caused by perma-frost or ice lenses.
The construction of typical friction piles for use in foundation construction or the construction of structural slabs and in the construction of vertical support members have certain inherent problems or negative characteristics such as:                A) In the case of friction piles which are drilled and the drilled hole is filled with concrete, the very heavy weight of the concrete must also be taken into account in calculating the load relative to the anticipated holding strength of the friction pile. Typically the piles have to be drilled deeper to take into account the fairly considerable additional weight of the pile itself.        B) Maximum friction or holding strength is achieved when as much of the surface of the concrete pile comes into contact with the wall of the drilled hole. This “contact” is not maximized whenever there is an occlusion in the wall of the concrete pile.        C) Concrete as a cementitious material is made with water and as such is susceptible to shrinkage as the concrete cures and any shrinkage of the concrete will lessen the skin friction of the pile. Curing time can also be a mitigating factor in slowing up the next stage of construction after the friction piles have been poured in place.        D) It is not atypical for piles to have to permeate a number of different strata of base soils and wherever the pile goes through a weak strata, the skin friction in this area will be significantly less thereby reducing the overall holding capacity of the pile and requiring a deeper pile to overcome this condition.        E) Wooden vertical support members although having a relatively low coefficient of heat transference, heat will still transfer through the wood and when placed in a perma-frost or ice-lens condition, eventual degradation of the perma-frost will occur        